This invention relates generally to ophthalmic compositions. In particular, the present invention relates to artificial tear compositions comprising the ionic components of normal human tear film in substantially the same amounts and proportions, as well as to methods for their preparation and storage.
The compositions of the present invention are also useful as lubricating and cushioning agents for the eye after traumatic injury or surgery. The present invention also relates to a method of treating eyes by topically applying the formulations of the present invention when indicated for the relief of dry eye syndrome and when indicated to achieve the other effects mentioned above.
Dry eye syndrome and related ailments, including transitory discomforts, are well known in the scientific and patent literature. These ailments have generally been treated by topical administration of any of a number of ophthalmic compositions. The currently marketed artificial tear compositions are listed on pages 504-504b of Drug Facts and Comparisons, New York: J. B. Lippincott Co., 1989. In general, these compositions contain salts, buffers and viscosity agents (e.g., hydroxypropyl methylcellulose, polyvinyl alcohol, Carbopol.RTM., a carboxy vinyl polymer). Most artificial tear compositions additionally contain preservatives (e.g., benzalkonium chloride, Dymed.RTM., a biguanide, and Polyquad.RTM., a polymeric quaternary ammonium compound), although some recently introduced compositions are non-preserved.
It has recently been determined that preservatives and non-physiologic ions which may be present in artificial tear compositions may be detrimental to the corneal epithelium. See, for example, Bernal et al., Current Eye Research, 10(7):645-656 (1991). There have therefore been attempts to develop non-preserved artificial tear compositions containing physiological tear components. See, for example, U.S. Pat. No. 4,775,531 (Gilbard); however, these formulations are based on the composition of rabbit tears and it has now been documented that human tears, although having the same types of ions, have distinctly different ion concentrations. See Rismondo et al., in The Contact Lens Association of Ophthalmologists, 15(3):222-229 (1989). In addition, although Gilbard's compositions list bicarbonate as an ingredient, bicarbonate is quite labile, since it is in equilibrium with carbon dioxide, and could escape from solution in a relatively short time.